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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Shuah Khan , Kuniyuki Iwashima , Hangbin Liu , Martin Karsten , Masashi Honma , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20261024153608.58569-1-leon.hwang@linux.dev> <20261024153608.58569-3-leon.hwang@linux.dev> Content-Language: en-US From: Leon Hwang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2026/10/25 09:19, Alexei Starovoitov wrote: > On Sat, Oct 24, 2026 at 08:36 AM Leon Hwang wrote: >> Instead of passing bpf log or extack to bpf_xdp_link_attach(), pass an >> errmsg pointer to receive the kstrdup() error msg, because > > [...] > >> 2) passing extack will access underlying driver string out of dev_put() >> guard, which will crash kernel when the device is unloaded >> concurrently. > > Netlink does exactly that. > rtnl_setlink() looks up the dev with __dev_get_by_index(), so no refcnt, > do_setlink() -> dev_change_xdp_fd(dev, extack, ...) calls into the same > drivers that set the same strings, rtnl is unlocked, and only then > netlink_rcv_skb() -> netlink_ack() does strlen(extack->_msg). > All extack users work this way. kstrdup() in one of them fixes nothing. Oops, I was overthinking about it when self-reviewing the patch. Failed to verify the describing crash issue just now. I should verify my review when self-reviewing. > > Instead of patches 1 and 2: > Will change like this. > > I'm think I gave this suggestion earlier. Why did you go with strdup()? > Sorry for my overthinking. Will verify my review to my patches in the future. Thanks, Leon